Optical scanning device

ABSTRACT

A laser bar code scanner employing a retroreflector in combination with a rotating polygon reflector to increase scan width and reduce curvature in the scanning beam.

This is a divisional of the prior application Ser. No. 08/893,336, filedJul. 16, 1997, U.S. Pat. No. 5,999,301.

FIELD OF THE INVENTION

The present invention relates generally to optical scanning devices, andmore particularly to a laser bar code scanner which folds the scan beamto generate a straight scan beam and increase scan beam width near thescanner.

BACKGROUND OF THE INVENTION

Laser bar code scanners employ a focused beam of light to repetitivelyscan across a bar code label. Typically, the scanning is produced bydynamic deflection of the source beam off of a rotating polygonreflector. Laser light reflections containing information from thescanned bar code are sensed in a photodetector. The bar code labelencodes information as a series of bars of various widths formed on acontrasting background. The difference between the reflectance of thebars compared to the spaces produces a modulated optical signal. Thedetected optical signal representing reflections from the label is thenconverted into an electrical signal by the photodetector and that signalis further processed and then decoded.

A general and long known problem with laser bar code scanners is thatthe width of the scanning beam becomes narrower the closer the scannedobject is to the scanner. The narrowing of the scanning area oftenrequires that the item to be scanned be positioned carefully in apredetermined target area to ensure that the bar code is properlyscanned.

One solution to reducing the above targeting constraint is to increasethe distance between the object to be scanned and the scanner. This maynot always be desirable. Also, there are circumstances in whichproximity between the scanner and the object to be scanned is essential.Another solution is to increase the optical path within the scanner sothat the exiting scan beam is wider. While this method is effective, itusually requires increasing the dimensions of the scanning device whichis usually undesirable, and can make the device entirely impractical fora number of applications.

One solution to the problem of widening the scanning area close to thescanner is to use a beam folding mirror to increase the optical pathwithin the scanner housing, thereby increasing the scanning width,without commensurate increase in size of the scanner. However, whilefolding mirrors work quite well in other applications, including camerasand telescopes, mirrors introduce optical path distortion when used inconjunction with scanning reflectors (e.g. rotating polygon scanreflectors). One of the most serious problems is the generation of acurved scanning beam.

The curved scanning beam is commonly referred to as either a “sad” or“smile” face scan beam pattern. The “sad” or “smile” face scan patternis generated by the distance translation of a rotating polygon reflectorand a flat fold mirror about the polygon.

There is a need for a compact laser bar code scanner that produces awide scanning area even when object to be scanned is placed close to thescanner. There is a further need that the beam have a flat,non-distorted scanning beam that can be produced by a compact laser barcode scanner that is reliable and economical to manufacture.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a retroreflectoris incorporated after a moving reflector so as to increase the width ofthe scanning beam and eliminate the curvature of the scan pattern. Theretroreflector increases the scanning area width by folding, therebyeffectively lengthening, the optical path within the scanner housing.Through the use of this technique it is possible to produce a compactscanner which, for example, can produce a scan width of 4 inches at adistance of 2 inches from the scanner.

The retroreflector may, for example, be a 90 degree prism, a cornercube, or two plane mirrors forming 90 degrees. A dynamically reflectedbeam from a moving reflector enters the retroreflector in one plane andexits in another plane in the opposite direction and parallel to theentering beam. Thus, the input beam from a light source forming a 90degree angle with the vertical side of the scanning reflector facet willexit at 90 degrees after folding from the retroreflector and without anyscanning beam curvature.

In the preferred embodiment the optical component of the presentinvention are held in position by a unitary mounting structure, alsoreferred to as an “optical bench”, which eliminates the need foradjusting the optical system. The optical bench not only eliminates theneed for tuning the optical system but increases the stability of thesystem over time. The optical bench may be manufactured from any numberof well known materials including metals, plastics, and ceramics. Anadditional benefit is that the optical bench can be die cast orinjection molded which reduces the fabrication costs.

As discussed, the laser scanning system is based upon a rotatingpolygon. In the preferred embodiment the laser is of a type having amultiple quantum well design. The size of the polygon is dictated by thetype of motor used, and the particular dimensions will depend uponrotation speed of the motor and the desired scan width. In the preferredembodiment the polygon has between 8 and 12 facets.

The present invention significantly improves upon the prior art byallowing the construction of a compact scanning device with a foldedoptical path providing an increased scanning width without sufferingbeam curvature. These and other features of the present invention willbe more fully appreciated when considered in light of the followingdetailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded detail view of the components of the presentinvention.

FIG. 2 isometric view of the polygon reflector and retroreflector systemdirecting a laser scan line.

FIG. 3 is a functional diagram of how beam curavture is infduced by aplane fold mirror.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a lower housing section 2 into which is fitted aprimary printed circuit board 4 and photo detector printed circuit board6. Primary printed circuit 4 is provided with a control integratedcircuit 8 and data port 10. Optical bench 14 is centrally mounted onprimary printed circuit board 4 and a motor spacer 12 is mounted on topof the optical bench 14. Optical bench 14 is further comprised of lasermounting support 16 and retroreflector mounting support 18. Aretroreflector 20 is mounted upon an upper portion or appendage 21 ofretroreflector mounting support 18 and is provided with a lowerreflector 22 and an upper reflector 24. A laser 26 is detachably mountedon an appendage 17 of the laser mounting support 16. A polygon reflectormotor 28 is mounted on appendages 19 which, in turn, are positioned onthe motor spacer 12 and opposite the laser mounting support 16 andretroreflector mounting support 18. A polygon reflector 30 is detachablymounted on polygon reflector motor 28. The optical bench 14 holds laser26, polygon reflector 30, and retroreflector 20 in optical alignment andremoves the need for adjusting the optical system. Housing gasket 32,which includes housing window frame 34, is circumferentially mounted ontop of lower housing section 2. Upper housing section 36 mounts on topof housing gasket 32 and housing window 38 mounts within housing windowframe 34.

FIG. 2 illustrates the device in operation where laser 26 produces afocused beam of light b which is projected onto polygon reflector 30.The beam b is deflected by polygon reflector 30 towards the lowerreflector 22 of retroreflector 20, the beam b is then reflected up toupper reflector 24 where it is then reflected out of the scanner. In thepreferred embodiment this arrangement can produce a 4 inch wide scanningbeam at 2 inches in a device that measures less than 3 inches on a side.

FIG. 3 illustrates how curvature results from the use of a rotatingpolygon reflector in conjunction with a plane fold mirror. By usingretroreflector 20 angle α goes to 0 and the beam is flattened.

From the foregoing teachings, it can be appreciated by one skilled inthe art that a new, novel, and nonobvious optical scanning device hasbeen disclosed. It is to be understood that numerous alternatives andequivalents will be apparent to those of ordinary skill in the art,given the teachings herein, such that the present invention is not to belimited by the foregoing description but only by the appended claims.

We claim:
 1. An optical scanning device comprising: a base structurehaving a main body portion and multiple appendages forming a first fixedmounting support, a second fixed mounting support, and a third fixedmounting support, wherein said base structure has a central region fromwhich extends a first appendage which forms said first mounting support,second and third appendages which form said second mounting support, anda fourth appendage which forms said third mounting support; aretroreflector having a light receiving surface and a light transmittingsurface attached to said first mounting support; a rotating polygonreflector positioned at said second mounting support so as to reflectlight onto said light receiving surface; an optical scanning beam sourceattached to said third mounting support and positioned so as to projectlight onto said rotating polygon reflector so that the beam is reflectedonto said light receiving surface; and wherein said base structure isconfigured such that said first, second and third fixed mountingsupports locate said retroreflector, said rotating polygon reflector,and said optical scanning beam source at the vertices of a triangle. 2.The device of claim 1, wherein said first appendage is of a shape andconfiguration to provide a scanning beam reflected by said lighttransmitting surface with a clear line of sight to an object to bescanned.
 3. The device of claim 1, wherein said second and thirdappendages are of a shape and configuration to provide a scanning beamreflected by said rotating polygon reflector with an unobstructedoptical path to the light receiving surface of said retroreflector. 4.The device of claim 1, wherein said fourth appendage is of a shape andconfiguration to provide a scanning beam produced by said opticalscanning beam source with an unobstructed optical path to the rotatingpolygon reflector.